In particular, image display systems such as video projectors utilize liquid crystal devices (LCD) acting as a programmable electromagnetic wave (EMW) field vector orientation rotating device ("PEMFVORFD") for displaying a projected image. A PEMFVORD for a video projector is typically formed as a LCD having a matrix of individual cells or pixels (picture elements) arranged in a checkerboard array. In general, the LCD is placed in a polarized (a single orientation of the electromagnetic wave electric field vector) light path and control is effected by altering the optical transmission characteristics (i.e., the birefringence) for each cell by the response to an applicable stimulus. The individual cells alter the polarization (change by rotating the polarization state or orientation of the electromagnetic wave electric field vector) of the individual cells or pixels according to the information that is desired to be finally portrayed as the projected image. The resolution of the projected image depends upon several factors, including the number of cells in the LCD. A display of 320 horizontal pixels by 240 vertical pixels will have a generally rectangular peripheral shape and yield a display of 76,800 pixels. A typical television set for the United States market is composed of 115,000 pixels (i.e., combination of red, blue and green dots in a television receiver). A light aperture for admitting light to the array of cells for the display generally is of a rectangular shape. Thus, it is important that the illumination is evenly distributed over a predetermined shape with a large degree of efficiency.
A LCD cell includes a liquid crystal material that is contained between two transparent plates.
A twisted nematic LCD cell requires the light incident at the LCD cell to be of even illumination so that the picture to be eventually displayed has an even illumination, especially important because of the large format of the picture that is eventually displayed. The polarized light for a typical projector is generally derived from a randomly polarized light source that is collimated.
The development of PEMFVORD technology has resulted in the development of LCD projectors which utilize one or more LCDs to alter the orientation of the electric field vector of the light being projected. A typical liquid crystal light valve ("LCLV") projector includes a source lamp which is used to generate a light beam that is directed through a polarizer. This polarized light is directed through the LCDs to change the polarization according to the image to be displayed. The light, after exiting the LCD, passes through a plastic polarizer analyzer which stops and absorbs the unwanted portion of light. The formed image is then enlarged with a projection lens system for forming an enlarged picture on a display screen. Any type of divergence in the light causes a loss in the brightness of the projectors, as this light does not pass through all of the optical components in the system as is not used for the final display, and must be removed through one of several methods.
Color LCLV projectors typically include color separating apparatus such as a prism, beam splitters or dichroic mirrors to separate collimated white light beams from the light source into three primary color beams, i.e., red, green and blue beams. The red, green and blue beams are then individually modulated by LCDs and combined by separate optical apparatus such as combining prisms, mirrors or lenses.
In general, the quality and brightness of the projected image in any liquid crystal light valve (LCLV) projector is a function of the brightness of the source for illuminating the LCDs and the polarizing means. Polarizing optics must be utilized to filter/separate the white light into light with a single orientation of the electric field vector. The white light emitted from the source is thus only partially utilized (i.e., one direction of polarization) in most LCLV projection systems. This requires oversized light sources to achieve a desired brightness at the viewing screen.
Moreover, the unused portion of light from the light source is absorbed and generates wasted energy in the form of heat and transfers this heat to other components (i.e., LCDs, electronics, etc.) and hence is detrimental to the system. This heat must be either shielded and/or dissipated from the components of the system, or else, the light source must be reduced in light output so that the amount of light being absorbed is below the threshold of permanent damage to the components.
Representative prior art LCLV projectors are disclosed in U.S. Pat. No. 5,060,058 to Goldenberg, et al, U.S. Pat. No. 5,048,949 to Sato, et al., U.S. Pat. No. 4,995,702 to Aruga, et al., U.S. Pat. No. 4,943,154 to Miyatake, et al., U.S. Pat. No. 4,936,658 to Tanaka, et al., U.S. Pat. No. 4,936,656 to Yamashita, et al., U.S. Pat. No. 4,935,758 to Miyatake, et al., U.S. Pat. No. 4,911,547 to Ledebuhr, U.S. Pat. No. 4,909,601 to Yajima, et al., U.S. Pat. No. 4,904,061 to Aruga, et al., U.S. Pat. No. 4,864,390 to McKechnie, U.S. Pat. No. 4,861,142 to Tanaka, et al., U.S. Pat. No. 4,850,685 to Kamakura, U.S. Pat. No. 4,842,374 to Ledebuhr, U.S. Pat. No. 4,836,649 to Ledebuhr, et al., U.S. Pat. No. 4,826,311 to Ledebuhr, U.S. Pat. No. 4,786,146 to Ledebuhr, U.S. Pat. No. 4,772,098 to Ogawa, U.S. Pat. No. 4,749,259 to Ledebuhr, U.S. Pat. No. 4,739,396 to Hyatt, U.S. Pat. No. 4,690,526 to Ledebuhr, U.S. Pat. No. 4,687,301 to Ledebuhr, U.S. Pat. No. 4,650,286 to Koda, et al., U.S. Pat. No. 4,647,966 to Phillips, et al., U.S. Pat. No. 4,544,237 to Gagnon, U.S. Pat. No. 4,500,172 to Gagnon, U.S. Pat. No. 4,464,019 to Gagnon, U.S. Pat. No. 4,464,018 to Gagnon, U.S. Pat. No. 4,461,542 to Gagnon, U.S. Pat. No. 4,425,028 to Gagnon, U.S. Pat. No. 4,191,456 to Hong, et al., U.S. Pat. No. 4,127,322 to Jacobson, et al., U.S. Pat. No. 4,588,324, to Marie, U.S. Pat. No. 4,943,155 to Cross, Jr., U.S. Pat. No. 4,936,657 to Tejima, et al., U.S. Pat. No. 4,928,123 to Takafuji, U.S. Pat. No. 4,922,336 to Morton, U.S. Pat. No. 4,875,064 to Umeda, U.S. Pat. No. 4,872,750 to Morishita, U.S. Pat. No. 4,824,210 to Shimazaki, U.S. Pat. No. 4,770,525 to Umeda, et al., U.S. Pat. No. 4,715,684 to Gagnon, U.S. Pat. No. 4,699,498 to Naemura, et al., U.S. Pat. No. 4,693,557 to Fergason, U.S. Pat. No. 4,671,634 to Kizaki, et al., U.S. Pat. No. 4,613,207 to Fergason, U.S. Pat. No. 4,611,889 to Buzak, U.S. Pat. No. 4,295,159 to Carollo, et al.
Prior art illumination systems for overcoming problems with the brightness of LCD display illumination systems have not been completely successful.
An example of an illumination system that attempts to utilize the full output of a light source for increasing the brightness of an LCD display is disclosed in U.S. Pat. No. 5,028,121 to Baur, et al. In the Baur system, the randomly polarized light source is resolved into two separate polarized beams, with one of the polarized beams passed to a dichroic color splitter that then directs the segregated color beams to a set of reflecting LCDs, while the other beam of different polarization is sent to a different set of LCDs through a different dichroic splitter. After having each respective portion of the beams' electric field vector altered, the beam is then reflected back through the dichroic mirrors into the polarizing beam splitter/combiner. The picture to be represented is sent to the projection lens, while the rejected beam is sent back into the light source. This causes the light source to heat and have a shortened life span. Furthermore, each sequential field to be projected has a different brightness level illuminating each pixel, depending upon the amount of light that is rejected back into the light source.
For example, if a light source has an average output of 1000 lumens and the sequential field to be projected has an average brightness level of 30%, then 700 lumens would be reflected back into the light source, making the light emitted from the source to be an effective 1700 lumens. In the next sequential field, if the average brightness level is 50%, then 500 lumens would be reflected back into the light source, making the light emitted from the source to be an effective 1500 lumens. This can be alleviated by computing the average brightness level to be projected, and then modulating the brightness level of the light source when the field is changed for projection so that the illumination of a pixel is at a constant brightness. This system can further be modified by (or be a stand alone system) that would monitor the light output of the light source and change the driving circuitry of the light source to maintain a constant brightness level. This can be monitored by a light transducer that monitors the light from a beam splitter, or alternately, can be mounted directly on a LCD panel outside of the picture forming active area. However, the addition of any of the above circuitry further complicates the projector and makes the light source an active part of the system, increasing the cost and complexity of the projector.
Another example of an illumination system that attempts to utilize the output of a light source for increasing the brightness of an LCD display is disclosed in U.S. Pat. No. 4,913,529 to Goldenberg, et al. In the Goldenberg system, a beam of light, from a light source, is split into two orthogonally linear polarized beams. One of the beams is then passed through a device that rotates one of the beams to change its direction of polarization so that there are two beams of the same polarization. The beams of the same polarization are then directed through different faces of a prism, combined by the prism and focused on the LCD devices.
A problem with such a system is that the beams are not collinear. The beams illuminate the polarizer at different angles, causing an area of usable light, and another area of unusable light. The result is that all of the light available is not used. Another obstacle is that it is difficult to align the combined beams with the use of a prism. Yet another complication is that the prism tends to separate the light into separate colors. This detracts from the clarity, brightness and limits the resolution of the projected image. Still another complication is that the performance of polarizers vary with the angle of light illuminating them, causing different polarizations and different color gradations to occur in the beam.
Other systems, such as those disclosed in U.S. Pat. No. 4,824,214 to Ledebuhr, U.S. Pat. No. 4,127,322 to Jacobson, et al., U.S. Pat. No. 4,836,649 to Ledebuhr, et al., and U.S. Pat. No. 3,512,868 to Gorklewiez, et al., also disclose optical layouts for achieving a high brightness in display systems that utilize LCD devices. In general, these systems are relatively complicated and contain numerous components that are large, expensive, and difficult to adjust.
Representative prior art flat fluorescent light sources are disclosed in U.S. Pat. No. 4,978,888 to Anandan, et al. and U.S. Pat. No. 4,920,298 to Hinotani, et al.
Representative prior art light integrators for light sources are disclosed in U.S. Pat. No. 4,918,583 to Kudo, et al., U.S. Pat. No. 4,787,013 to Sugino, et al. and U.S. Pat. No. 4,769,750 to Matsumoto, et al.
Various prior art techniques and apparatus have been heretofore proposed to present 3-D or stereographic images on a viewing screen and they also use a light source, and they also have the same problems as mentioned above. See U.S. Pat. No. 4,955,718 to Jachimowicz, et al., U.S. Pat. No. 4,963,959 to Drewio, U.S. Pat. No. 4,962,422 to Ohtomo, et al., U.S. Pat. No. 4,959,641 to Bess, et al., U.S. Pat. No. 4,957,351 to Shioji, U.S. Pat. No. 4,954,890 to Park, U.S. Pat. No. 4,945,408 to Medina, U.S. Pat. No. 4,936,658 to Tanaka, et al., U.S. Pat. No. 4,933,755 to Dahl, U.S. Pat. No. 4,922,336 to Morton, U.S. Pat. No. 4,907,860 to Noble, U.S. Pat. No. 4,877,307 to Kalmanash, U.S. Pat. No. 4,872,750 to Morishita, U.S. Pat. No. 4,870,486 to Nakagawa, U.S. Pat. No. 4,853,764 to Sutter, U.S. Pat. No. 4,851,901 to Iwasaki, U.S. Pat. No. 4,834,473 to Keyes, et al., U.S. Pat. No. 4,807,024 to McLaurin, et al., U.S. Pat. No. 4,799,763 to Davis, U.S. Pat. No. 4,772,943 to Nakagawa, U.S. Pat. No. 4,736,246 to Nishikawa, U.S. Pat. No. 4,649,425 to Pund, U.S. Pat. No. 4,641,178 to Street, U.S. Pat. No. 4,541,007 to Nagata, U.S. Pat. No. 4,523,226 to Lipton, et al., U.S. Pat. No. 4,376,950 to Brown, et al., U.S. Pat. No. 4,323,920 to Collendar, U.S. Pat. No. 4,295,153 to Gibson, U.S. Pat. No. 4,151,549 to Bautzc, U.S. Pat. No. 3,697,675 to Beard, et al. In general, these techniques and apparatuses involve the display of polarized or color sequential two-dimensional images which contain corresponding right eye and left eye perspective views of three-dimensional objects. These separate images can also be displayed simultaneously in different polarizations or colors. Suitable eyeware, such as glasses having different polarizing or color separating coatings, permit the separate images to be seen by one or the other eye. This type of system is relatively expensive and complicated requiring two separate projectors and is adapted mainly for stereoscopic movies for theaters. U.S. Pat. No. 4,954,890 to Park discloses a representative projector employing the technique of alternating polarization.
Another technique involves a timed sequence in which images corresponding to right-eye and left-eye perspectives are presented in timed sequence with the use of electronic light valves. U.S. Pat. No. 4,970,486 to Nakagawa, et al., and U.S. Pat. No. 4,877,307 to Kalmanash disclose representative prior art stereographic display systems of this type.